The objective of this research is to obtain an understanding of the role of lipids, especially the phospholipid polar head groups, in membrane structure and function. The main approach to be used in this research will be to alter the lipid composition with respect to the fatty acids, the polar head groups and the sterol content of cells in tissue culture. Subcellular membrane fractions, including the plasma membrane, endoplasmic reticulum, and mitochondria will be isolated from the cells with different lipid compositions. The changes in the lipid composition will be correlated with changes in the physical and biochemical properties of the membranes. The structure and fluidity of the membranes and reconstituted phospholipid vesicles containing membrane proteins will be studied by fluorescence polarization, energy transfer methods, and phase fluorometry. The properties of D-Beta-hydroxybutyrate dehydrogenase, cytochrome b5 and cytochrome b5 reductase will be examined in order to determine how lipids interact with them and affect their activity. Another aspect of the research will involve the properties of vesicular stomatitis virus and Rous sarcoma virus derived from cells with different lipid compositions in order to understand how these viruses acquire their unique lipid compositions. Along the same lines, the properties of lipoproteins secreted by primary rat hepatocyte cultures will be examined to determine if the lipoproteins selectively incorporate phospholipids. These studies should provide unique information on the contribution of lipids to the activity of membranous enzymes and to the organization and structure of animal cell membranes and viruses.